Automatic doors are in widespread use in various applications, such as elevators, buses, and trains. Considerations of personal safety require that doors are not to be closed when there is a danger that a person might be impacted thereby. While not compromising safety considerations, considerations of efficiency dictate that doors must be closed as promptly and quickly as possible. At the same time it is important that sensors, causing doors to close or alarming security systems to operate, should enable small changes in the environment and fixed patterns existence.
There exist various techniques and apparatus for sensing the existence of a person and his accouterments within a predefined zone and consequently operating an automatic door.
The following U.S. patents exemplify the state of the art:
No.TitleDateInventor(s)2,826,753Object DetectorsApr. 13, 1954Chapin4,029,176Doorway Safety DeviceJun. 14, 1977Gerald4,590,410Object SensingMay 20, 1986JonssonApparatus4,779,240Ultrasonic SensorOct. 18, 1988Dorr et al.System4,976,337Proximity DetectionDec. 11,TrettSystems19905,001,557Method of, andMar. 19, 1991BegleApparatus for,Controlling the Positionof an AutomaticallyOperated Door5,149,921Self Correcting InfraredSep. 22,PicadoIntrusion Detection1992System5,276,391Door Mounted SafetyJan. 4, 1994JonssonApparatus5,337,289Phased-Array UltrasonicAug. 9, 1994Fasching etSurface Contoural.Mapping System andMethod for SolidsHoppers and the Like5,412,297Monitored RadioMay 2nd, 1995Clark et al.Frequency Door EdgeSensor5,420,430Detection Systems forMay 30, 1995TrettDetecting Obstructionsin DoorwaysRE 33,668Detection Device HavingAug. 20, 1991GrayEnergy TransmittersLocated at VerticallySpaced Apart PointsAlong Movable DoorsRE 30,719Doorway Safety DeviceAug. 25, 1981Gerald
U.S. Pat. No. 5,412,297 teaches a tactile obstruction detector, while U.S. Pat. Nos. 4,590,410 and 5,276,391 concern optical detectors. Tactile detectors are prone to suffer from a high degree of tear and ware and thus have a very low reliability. Furthermore they require physical contact and more specifically that a minimum force be applied thereon to be tripped, which makes them unsuitable for many applications. Optical sensors are sensitive to lighting conditions and do not function under daylight. Moreover, they do not allow differentiating between objects at a close proximity since such differentiation requires a measurement capability in the magnitude of the speed of light for small divergences. U.S. Pat. No. 2,826,753, relates to object detection in a confined environment and not to door opening or closing, for example.
U.S. Pat. Nos. RE 30,719, and 4,029,176 describe acoustic energy-based detectors.
Other distance and direction measuring apparatuses are described in the following U.S. patents:
No.TitleDateInventor(s)5,319,611Method ofJun. 7, 1994KorbaDetermining RangeData in a Time-of-Flight Ranging System5,339,075Vehicular CollisionAug. 16, 1994Abst et al.Avoidance Apparatus5,341,344Obstacle-DetectionAug. 23, 1994O' Brien et al.System5,373,482Distance MeasuringDec. 13,GauthierSystem Arranged to1994Limit False Indicationsof DistanceMeasurements5,450,057Stereophonic WarningSep. 12,WatanabeApparatus19955,467,072Phased Array BasedNov. 14,MichaelRadar System For1995Vehicular CollisionAvoidance6,344,642Door ControlFeb. 5,Agam et al.Apparatus2002
A common problem with ultrasonic sensors from the prior art is that they do not allow covering a volume where the signal fades and varies along the path and differentiating a legitimate clutter signal from a penetration signal.
Indeed, when dealing with ultrasonic sensors or other ultrasonic devices, one has to consider the “picture” the device see, i.e. the volume that the device can detect. This volume of course, is measured in terms of electrical voltage, and will be referred to herein as the “clutter”.
The clutter of a sensor includes echoes received from objects located within the sensor's beam. These objects may include static objects, which the sensor always detects, and therefore should ignore, and dynamic objects, which the sensor detects periodically when they enter its beam. Those dynamic objects are considered relevant targets and should be detected by the sensor.
A drawback of sensing methods and apparatuses from the prior art is that they do not allow discriminating between static objects and relevant targets to be detected.